The　carbon　content　was　adjusted　in　the　raw　materials　used　to　synthesize　the　WC-Co　composite　powder　by　in　situ　reactions.　It　was　found　that　in　the　sintered　nanocrystalline　cemented　carbide　bulk,　the　matching　of　key　planes　(0001),　(10-10)　and　(10-11)　was　influenced　by　the　carbon　content.　The　matching　relationship　plays　an　important　role　in　the　mechanical　properties　of　the　bulk　material　along　certain　directions.　At　an　optimized　carbon　content　of　16.09　wt%　for　the　WC-6Co　cemented　carbide,　both　high　hardness　(2130　kg　mm(-2))　and　high　toughness　(11.8　MPa　m(1/2))　were　achieved　simultaneously.